. relations to various exigencies of the Animal Body. 61 



" that in the cases, at least of ordinary exercise 



of force, the exigencies of the respiratory system keep pace 

 more nearly with the demand for nitrogenous constituents of 

 food than is usually supposed/' 



And further : — 



" A somewhat concentrated supply of nitrogen does, however, 

 in some cases, seem to be required when the system is over- 

 taxed — as for instance, when day by day more labour is de- 

 manded of the animal body than it is competent without de- 

 terioration to keep up ; and perhaps also, in the human body, 

 when under excitement or excessive mental exercise. It must 

 be remembered, however, that it is in butchers' meat, to which is 

 attributed such high flesh-forming capacity, that we have also, 

 in the fat which it contains, a large proportion of respiratory 

 material of the most concentrated kind. It is found, too, that 

 of the dry substance of the egg, 40 per cent, is pure fat. 



"A consideration of the habits of those of the labouring 

 classes who are under- rather than over-fed, will show, that 

 they first have recourse to fat meat, such as pork, rather than 

 to those which are leaner and more nitrogenous — thus perhaps 

 indicating, that the first instinctive call is for an increase of the 

 respiratory constituents of food. It cannot be doubted, how- 

 ever, that the higher classes do consume a larger proportion of 

 the leaner meats; though it is probable, as we have said, that 

 even with these, as well as pork, more/atf, possessing a higher 

 respiratory capacity than any other constituent of food, is 

 taken into the system than is generally imagined. Fat and 

 butter, indeed, may be said to have about twice and a half the 

 respiratory capacity of starch, sugar, &c. It should be re- 

 membered, too, that the classes which consume most of the 

 leaner meats, are also those which consume the most butter, 

 sugar, and in many cases, alcoholic drinks also. 



"It is further worthy of remark, that wherever labour is 

 expended in the manufacture of staple articles of food, it has 

 generally for its object the concentration of the wow-nitro- 

 genous, or more peculiarly respiratory constituents. Sugar, 

 butter, and alcoholic drinks are notable instances of this. Cheese, 

 which at first sight might appear an exception, is in reality not 

 so ; for those cheeses which bring the highest price are always 

 those which contain the most butter; whilst butter itself is 

 always dearer than cheese. 



"In conclusion, it must by no means be understood that we 

 would in any way depreciate the value of even a somewhat 

 liberal amount of nitrogen in food. We believe, however, 

 that on the current views too high a relative importance is at- 

 tached to it ; and that it would conduce to farther progress in 



